1. Field of the Invention
The present invention relates to a damper with a variable damping force that is controlled by using a piston to divide an interior of a cylinder filled with a magnetic viscous fluid into a first fluid chamber and a second fluid chamber. The first fluid chamber and the second fluid chamber communicate with each other through a fluid passage formed to penetrate the piston. A coil provided with the piston is energized using a controller to change the viscosity of the magnetic viscous fluid in the fluid passage.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 60-113711 discloses a damper in which the viscosity of a magnetic viscous fluid (MRF: Magneto-Rheological Fluids) is changed by a magnetic field and used as the viscous fluid by the damper of a suspension system having a variable damping force. A coil causes the magnetic field to act on the magnetic viscous fluid in the fluid passage and is provided with a piston that is slidably fitted in a cylinder. The damping force of the damper is controlled, as desired, by changing the viscosity of the magnetic viscous fluid in the fluid passage using the magnetic field generated by energizing the coil.
While the damper is able to secure a large variable area of the damping force, when it is impossible to energize a coil due to failure, the damping force is maintained at an extremely low level which increases the possibility of the riding comfort and driving stability of the vehicle to significantly deteriorate.